When Zhu Yuanzhang, the first Emperor of the Ming Dynasty (1368-1644), established Ming dynasty, he began to enlarge the wall built initially during the old Tang Dynasty (618 - 907), creating the modern Xian City Wall. It's the most complete city wall that has survived in China, as well being one of the largest ancient military defensive systems in the world. After the extension, the wall now stands 12 meters (40 feet) tall, 12-14 meters (40-46 feet) wide at the top and 15-18 meters (50-60 feet) thick at the bottom. It covers 13.7 kilometers (8.5 miles) in length with a deep moat surrounding it. Every 120 meters, there is arampart which extends out from the main wall. All together, there are 98 ramparts on the wall, which were built to defend against the enemy climbing up the wall. Each rampart has a sentry building, in which the soldiers could protect the entire wall without exposing themselves to the enemy. Besides, the distance between every two ramparts is just within the range of an arrow shot from either side, so that they could shoot the enemy, who wanted to attack the city, from the side. On the outer side of the city wall, there are 5,948 crenellations, namely battlements. The soldiers can outlook and shoot at the enemy. On the inner side, parapets were built to protect the soldiers from falling off. Initially, the wall was built with layers of dirt, with the base layer including also lime and glutinous rice extract. Throughout the time Xi’an City Wall has been restored three times.